Manufacture of electrical resistances.



A. W. MALEY.

MANUFACTURE OF ELECTRICAL RESISTANOES, APPLICATION FILED 1111.23, 1914.

1,118,906. Patented Nov. 24, 1914 (Z 2 f WM I j y E? e 2% 91 &2? FFLT%/ZQ 1-11-11 d t a 1 1 g a 11111 g a 11111 g a 11111 g a 11111 11w 11TH 6 cd 5 L ]']"]'H d a 11111 g a 11111 111 1 11111 g .3 11111 g a T1 1 1 1 1Nil- :1 W y iffirz axle; Inventor MW 1%. 25M fi w W SA I AEEEED WALTERMALEY, OF HANDSWORTH, BIRMINGHAM, ENGLAND.

MANUFACTURE OF ELECTRICAL RESISTANCES.

Specification of Letters Patent.

Patented Nov. 24-, 191d.

original application filed October 8. 1910, Serial no. 586,030. Dividedand this application filed January To all whom it may concern:

Be it known that l, ALFRED WALTER ltlnnnv, a subject of the King ofGreat Britain, residing formerly at 200'Beeches road, W'est Bromwich, inthe county of Staffor all those purposes where the use of this type isadvantageous.

lhis invention contemplates the manufacture of resistances which have tobe extremely rigid, Without forming said resistances from hard andtherefore dillicultly workable material.

The invention consists in shaping the resistance elements from materialwhile in an easily workable state and then transforming the materialinto a rigid and hard state.

More particularly defined the invention comprises a method of formingresistance elements into the required grid form from comparatively softmaterial and subsequently increasing the resistance uniformly throughoutthe length of the material and also increasing the rigidity of the gridby case hardening.

Further according to this invention a resistance grid is made up ofelements made by forming soft wire into the requisite shape andsubsequently case hardening the wire.

The invention yet further comprises a method of forming rheostats bystamping the resistance elements thereof from comreference letters referto corresponding Serial No. 813,881.

parts, the wire a of proper cross section and of comparatively softmaterial is wound into a continuous zigzag in the manner of a series ofgrids as seen in Fig. 1 and as claimed in my co-pending patentapplication Serial No. 586,030 filed October 8, 1910. This material maythen be hardened by carbonization by the well known process of casehardening which causes an increase in the specific resistance of thewire resulting from the addition of carbon. Successive sections are, astherein described, bent parallel or approximately parallel to each otheras bestshown in Fig. 2, the wires being twisted at the bend so that thedepending loop 6 is flat on its outer surface to receive terminals atthe bends for tappings to external circuits. The grids are supported onbolts a surrounded by insulating tubes 0 and are separated from eachother by insulating washers (Z. The bolts 7) are clamped at their endsby means of nuts to a pair of parallel frame plates.

Where the resistance is formed, as above described from wires of softmaterial which are subsequently case hardened to increase the resistanceand rigidity of the rheostats, it is not necessary to adhere to the gridtype, although this is the best known and is very compact. Instead thewire or rod can be wound in flat coils, but this has the disadvantagethat one end is in the middle. This disadvantage can, however, beavoided by forming the soft material by winding the strip over a sheetand then removing the sheet so that the rheostat remains airinsulated.Such coils may be mounted in the same way as known types of grid.

Commonly in stamping grids a diliiculty is encountered owing to the factthat the strength necessary in the stamping tool dotermines the size ofthe latter, and this again determines the minimum size of openingbetween successive turns of the grid. This becomes particularlyimportant when material of higher specific resistance is employed, forin this case a greater thickness of material is required and a morespecific tool becomes necessary. The method of making grids as shown inFig. 4 overcomes this difliculty. Therein the grid is stamped from thecomparatively soft material in the form of a simple open sinuous strip(Fig. 4) which will allow of the use of adequately large tools even forstamping fairly thick material. As shown, a strong Wedge-shaped tool mayoperate between the side portions h. The sinuous strip 9 thus formed canbe closed up by bending While still comparatively soft so that its turnslie close beside one another as in the ordinary grid. Then theresistance and rigidity of the grid is in creased by the case hardeningprocess. Of course continuous grids as shown in Figs. 1 to 3 may also beformed in this fashion.

What I claim is:

1. A method of making resistance elements consisting in forming aresistance element into the required form from compara tively softmaterial and increasing the rigidity of the element and the resistanceuniformly throughout the length of the material by subsequently casehardening the same.

2. A method of making resistance elements having a large carboncontentsconsisting in stamping resistance elements of the desired formfrom soft iron and subsequently heating said elements in carbon in orderto eifect case hardening thereof to thereby increase the rigidity of theelement and the resistance uniformly throughout the length of theelement.

3. A method of making resistance elements having a large carbon contentconsisting in stamping simple open sinuous strips from soft iron,closing up said strips to the desired grid form, and subsequentlyheating said elements in carbon in order to effect case hardeningthereofto thereby increase the rigidity of the element and theresistance uniformly throughout the length of the element.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing Witnesses.

ALFRED WALTER MALEY.

Witnesses JoHNsoN CODBURY, KATHLEEN M. THOMPSON.

